The goal of the proposed research is to study the control of immunoglobulin gene expression in mammalian cells by examining induced mutations in mouse myeloma cell lines. Some variants have been isolated and others will be selected from cloned cells with an anitbody-overlay procedure which uses antisera directed against specific antigenic determinants of secreted immunoglobulins. Variants will be characterized by electrophoresis of radiolabeled immunoglobulin products on acrylamide gels containing sodium dodecyl sulfate, by serological analysis, and by ion exchange chromatography. We will examine the types of variants induced by different drugs especially those used in the chemotherapy of multiple myeloma. We hope to isolate variants synthesizing immunoglobulins with changes in the antigen-binding site. We will explore the relationship of primary and secondary variants and the effect on gene expression of various treatments, such as passage of variant tumors through animals and incubation of cells with anti-immunoglobulin reagents. A considerable portion of our efforts will be devoted to the structural analysis of altered heavy immunoglobulin chains. We will approach this goal through the isolation of the CNBr fragments of the parent molecule and through the development of analytical techniques for the various fragments. In this way, we will pinpoint the specific sites of mutation in the variant molecules and then focus detailed structural analysis on those segments.